The electrical power industry has many requirements for medium power, such as the 15 amp range, two-position switching devices that provide contacts which when opened or closed, stay in the selected position. These positions are mechanically held or maintained until a subsequent operation causes a change. Ordinarily manually operated rotary switches or remote operated relays are used to provide the maintained contacting. Although rotary switches and remote operated relays can have contacts of equal electrical rating and can operate between two functional positions, these devices are not directly interchangeable.
For example, manually operated rotary switches can provide a large number of electrical contacts that can be maintained in either position but are not designed to operate between positions by remote control. Conventional electromechanical relays operate by remote control, i.e. activation of an electric power source, between two positions (operate or release for example) but typically do not provide for a large number of contacts. Moreover, relay devices often do not provide maintained contacts because coil power to the relays has to be supplied constantly to hold normally opened contacts closed. Also, the relay design is such that conventional devices do not provide for manual operation.
In many cases electric power systems designs include both relays for remote operation and separate manually operated rotary switches. This can result in redundancy in switching schemes which adds to expense and system complexity sometimes with reduced reliability.
It is now recognized that it is desirable to have a single switching device which has the characteristics of both a manually operated rotary switch and a remote operated latching relay which device is called a latching switch relay in this specification.